diff --git a/llvm/lib/Transforms/Vectorize/SLPVectorizer.cpp b/llvm/lib/Transforms/Vectorize/SLPVectorizer.cpp
--- a/llvm/lib/Transforms/Vectorize/SLPVectorizer.cpp
+++ b/llvm/lib/Transforms/Vectorize/SLPVectorizer.cpp
@@ -283,6 +283,26 @@
   return false;
 }
 
+/// Checks if the given value is actually an undefined constant vector.
+static bool isUndefVector(const Value *V) {
+  if (isa<UndefValue>(V))
+    return true;
+  auto *C = dyn_cast<Constant>(V);
+  if (!C)
+    return false;
+  if (!C->containsUndefOrPoisonElement())
+    return false;
+  auto *VecTy = dyn_cast<FixedVectorType>(C->getType());
+  if (!VecTy)
+    return false;
+  for (unsigned I = 0, E = VecTy->getNumElements(); I != E; ++I) {
+    if (Constant *Elem = C->getAggregateElement(I))
+      if (!isa<UndefValue>(Elem))
+        return false;
+  }
+  return true;
+}
+
 /// Checks if the vector of instructions can be represented as a shuffle, like:
 /// %x0 = extractelement <4 x i8> %x, i32 0
 /// %x3 = extractelement <4 x i8> %x, i32 3
@@ -350,7 +370,7 @@
       return None;
     auto *Vec = EI->getVectorOperand();
     // We can extractelement from undef or poison vector.
-    if (isa<UndefValue>(Vec))
+    if (isUndefVector(Vec))
       continue;
     // All vector operands must have the same number of vector elements.
     if (cast<FixedVectorType>(Vec->getType())->getNumElements() != Size)
@@ -4786,7 +4806,7 @@
               return !is_contained(E->Scalars,
                                    cast<Instruction>(V)->getOperand(0));
             }));
-        if (isa<UndefValue>(FirstInsert->getOperand(0))) {
+        if (isUndefVector(FirstInsert->getOperand(0))) {
           Cost += TTI->getShuffleCost(TTI::SK_PermuteSingleSrc, SrcVecTy, Mask);
         } else {
           SmallVector<int> InsertMask(NumElts);
@@ -6151,7 +6171,7 @@
         V = Builder.CreateShuffleVector(V, Mask);
 
       if ((!IsIdentity || Offset != 0 ||
-           !isa<UndefValue>(FirstInsert->getOperand(0))) &&
+           !isUndefVector(FirstInsert->getOperand(0))) &&
           NumElts != NumScalars) {
         SmallVector<int> InsertMask(NumElts);
         std::iota(InsertMask.begin(), InsertMask.end(), 0);
diff --git a/llvm/test/Transforms/SLPVectorizer/X86/insert-element-build-vector-const-undef.ll b/llvm/test/Transforms/SLPVectorizer/X86/insert-element-build-vector-const-undef.ll
--- a/llvm/test/Transforms/SLPVectorizer/X86/insert-element-build-vector-const-undef.ll
+++ b/llvm/test/Transforms/SLPVectorizer/X86/insert-element-build-vector-const-undef.ll
@@ -18,8 +18,7 @@
 ; CHECK-NEXT:    [[TMP7:%.*]] = insertelement <2 x float> [[TMP6]], float [[B1]], i32 1
 ; CHECK-NEXT:    [[TMP8:%.*]] = select <2 x i1> [[TMP3]], <2 x float> [[TMP5]], <2 x float> [[TMP7]]
 ; CHECK-NEXT:    [[TMP9:%.*]] = shufflevector <2 x float> [[TMP8]], <2 x float> poison, <4 x i32> <i32 0, i32 1, i32 undef, i32 undef>
-; CHECK-NEXT:    [[RB1:%.*]] = shufflevector <4 x float> <float poison, float poison, float undef, float undef>, <4 x float> [[TMP9]], <4 x i32> <i32 4, i32 5, i32 2, i32 3>
-; CHECK-NEXT:    ret <4 x float> [[RB1]]
+; CHECK-NEXT:    ret <4 x float> [[TMP9]]
 ;
   %c0 = extractelement <4 x i32> %c, i32 0
   %c1 = extractelement <4 x i32> %c, i32 1